1. Field of the Invention
The invention relates to a method of manufacturing a jet nozzle plate for an ink jet printing head, utilizing a base plate in which there is provided a bore in order to form a jet nozzle, said bore having a diameter which is larger than the internal diameter of the ultimate jet nozzle, the base plate being subsequently covered as a whole unit, as far as into the bore, with a layer of a chemically depositable material.
2. Description of the Prior Art
A method of this kind is described in IBM Technical Disclosure Bulletin, Vol. 15, No. 9, pages 2845 and 2846. The base plate thereof is provided with a bore in which a wire is concentrically inserted, the diameter of said wire corresponding to the inner diameter of the ultimate jet nozzle, after which the base plate is covered as a whole unit, as far as into the bore, with a layer of a material which is chemically deposited, after which the wire is removed by etching so that the jet nozzle is cleared. A given length of the wire projects from the bore, so that material is also deposited thereon and a jet nozzle is formed which consists of a tube whose free end projects from the jet nozzle plate. A method of this kind is not easy to perform, particularly in view of the centering of the wire in the bore.
For the formation of a jet nozzle plate where a jet nozzle is formed by a tube whose free end projects from the jet nozzle plate, it may be stated that even though favorable properties are thus obtained as regards the ejection of droplets of ink from such a jet nozzle plate, it is difficult to cap the jet nozzle exactly with a capping device when the jet nozzle is out of operation, for example, in the rest condition of the ink jet printing head, in order to prevent drying of the ink in the jet nozzle and hence clogging of the nozzle so that it can no longer be used. This difficulty arises inter alia because the capping device, customarily consisting of a slightly elastic cushion, is not exactly flatly arranged against the end face of the tube but is curved around this end, so that it does not completely cover the jet nozzle. In this respect German Auslegeschrift 23 62 576 proposes an embodiment of the jet nozzle plate in which an annular trough is provided around a jet nozzle, said trough being adjoined by a dam having a plane surface which is situated at the same level as the end face of the jet nozzle which itself is also tubular. However, said German Auslegeschrift 23 62 576 does not describe how such a jet nozzle plate can be efficiently manufactured.
It is the object of the invention to provide a method of manufacturing a jet nozzle plate of the kind set forth where a jet nozzle which is formed by a tube is surrounded by an annular trough which is adjoined by a dam having a plane surface. The execution of such a method should be as simple as possible, but it should also be ensured that a jet nozzle plate of this kind can be very accurately manufactured.
To this end, the method in accordance with the invention is characterized in that prior to the covering of the base plate, consisting of a selectively chemically etchable material, preferably brass, with the layer which consists preferably of nickel, on the front thereof there is milled a recess which surrounds the bore mainly concentrically at a distance after which the layer is deposited with a thickness which defines the inner diameter of the bore to the inner diameter of the ultimate jet nozzle, after which the front of the base plate is ground down by an amount which at least equals the thickness of the layer but which is smaller than the sum of the thickness of the layer and the depth of the recess, after which the base plate is etched from the front to remove the material of the base plate exposed by the grinding operation until the layer projecting from the bore forms a freely projecting cylindrical tube which is surrounded by an annular trough. Thus, using technologically suitably controllable methods, at the same time the jet nozzle consisting of a free end of a tube is formed as well as a dam which extends at a distance from the jet nozzle, determined by an annular trough, and which serves as a bearing surface for a capping device. The surface of the dam extends exactly in the same plane as the end face of the free end of the tube, so that particularly accurate capping of the jet nozzle by means of a capping device is possible.
It has been found that the recess surrounding a bore is preferably formed as a circular ring by milling. The recess can thus be simply and accurately formed by means of an end-milling cutter.
It has also been found that the recess surrounding a bore is preferably formed by the milling of straight grooves which together form a polygon. The recess can thus be simply formed by means of a side-milling cutter.
Using a method as described above, for example, the recess surrounding a bore can be milled to a depth which is smaller than the thickness of the layer subsequently deposited thereon. Because the amount by which the front of the base plate must be ground down must be larger than the thickness of the layer but smaller than the sum of the thickness of the layer and the depth of the recess, grinding may be comparatively critical in the above case when the depth of the recess is small. Therefore, it has been found that the recess surrounding a bore is preferably milled to a depth which is greater than the thickness of the layer subsequently deposited thereon, after which the front of the base plate is ground down so far that the layer present in the recess is also slightly ground. The amount of grinding is thus larger, so that the grinding operation can be better controlled. Because grinding is continued until the layer present in the recess is also slightly ground, it is achieved that no raised edges which could distrub the suitable capping of the jet nozzle remain along the edges of the layer present in the recess.
It has also been found that a further recess which has the same depth as the recess surrounding a bore is preferably milled along the edge of the base plate. Thus, without the method becoming more complex, at the area of the edge of the jet nozzle plate an additional dam is formed as a bearing surface for a capping device which also benefits the capping of a jet nozzle.
For a method of manufacturing a jet nozzle plate comprising at least two adjacent jet nozzles it has been found that the recesses surrounding the adjacent bores are preferably milled to change over into one another. The dams thus form a coherent bearing surface around the jet nozzles, which also has a favorable effect on the capping of the jet nozzles with a capping device.
It has also been found that the recess surrounding a bore is preferably extended to the edge of the base plate by further milled recesses which have the same depth as the recess surrounding the bore. Thus, a dam having a maximum bearing surface for a capping device is obtained, so that a jet nozzle can be particularly accurately capped.